Why Are My Cucumber Leaves Turning Yellow? Direct Answer (2023)

Cucumbers are probably one of the most popular and widespread crops in domestic gardens. Available in numerous varieties, they are prepared in a variety of ways and can be grown outdoors or in a greenhouse. While the fruiting vegetable is one of the best species of the family to grow in cooler regions, that doesn’t protect them from disease and deficiency.

A common problem of the cucumber plant is yellow leaves, which can have various causes.  Despite their high level of fame and popularity, it happens again and again that the leaves of the plants turn yellow, and sometimes, if you act incorrectly or too hesitantly, the entire plant dies.

To prevent this from happening, here are the most common causes of cucumber leaves turning yellow, as well as simple and safe ways to remedy them.

Why are my cucumber leaves turning yellow?

Cucumbers are one of the fast-growing plants. This almost inevitably results in very low resistance to adverse environmental conditions, but also to diseases and other pests. Due to its rapid growth, the plant can build up much less protection in the form of plant skin and the general constitution of the plant than slow-growing plants can.

1. Incorrect or lack of care 

The most common reason for yellow cucumber leaves is probably not pest infestation or disease, but mainly in the area of care. Because if too much or little care is taken, or even the wrong care measure is chosen, this has a direct effect on the entire plant and usually shows its effects within a very short time.

Especially when growing in the greenhouse, almost all yellow leaves can be traced back to care errors. This is mainly because the greenhouse offers a fairly good level of protection from pests and airborne diseases.

These things are commonly done wrong and result in yellow leaves on cucumbers:

i) Incorrect ventilation

Constant air exchange is important, especially in the greenhouse, but strong drafts are disadvantageous because the leaves dry out and the temperatures change quickly.

Strongly fluctuating air humidity: mainly due to drafts and uneven watering – leads to dehydration (if too little) or increased mold infestation (if too much), as well as inhibited growth due to fluctuating conditions.

ii) Uncontrolled permanent ventilation of the greenhouse

Permanently constant ventilation without adjustment to the position of the sun etc. leads either to overheating during the day or to severe cooling at night.

As a result, often turns yellow and sometimes dies, since cucumbers in greenhouses are accustomed to uniform conditions.

iii) Too low soil temperatures

• Temperatures below 10°C damage roots, but here too the first symptoms are yellow leaves.
• Occurs mainly when the greenhouse cools down too much and there is a lack of protection in the event of unexpected frost.
• Planting distance too small:  plants standing close together hinder each other’s growth and compete fiercely for light and water.
• Due to undersupply, the plant dies, beginning with yellowing leaves.

Contaminated or germ-infested soil without sufficient drainage capacity: when using “used” soil, germs, and pests often enter, especially in greenhouses, with insufficient drainage capacity, for example through foundations, etc. of the greenhouse. so there is also the danger of rotting and dying of the cucumbers due to waterlogging

2. Fungi and parasites

In the protected environment of a greenhouse, mostly incorrect care of the plants becomes a problem, outdoors there is a real danger caused by fungi, germs, and other pests. Because outdoors, the protective glass shell is missing, which usually effectively keeps fungal spores and pest migration away or at least hinders them. Once a cucumber plant is infected, without quick and targeted countermeasures, this will quickly lead to cucumber leaves developing a yellow color and sometimes the entire plant dying. 

These diseases and parasites are particularly common in cucumbers:

i) Cucumber powdery mildew

• Caused by fungal infestation
• Visually resembling whitish floury spots,
• Later flat white coating over the entire plant

ii) Cucumber mosaic virus

• Viral disease that can be recognized by yellowing of the leaves from the leaf edges
• Optically, depending on the stage, partially or over the entire leaf mosaic-like spots are seen in different shades of green, brown and yellow

iii) Aphids

• Yellow leaves due to bitten ducts in the leaves and  drying out
• Recognizable as a few millimeters in size, mostly green-yellowish to brownish insects with an elongated body and a pronounced proboscis for drilling into the plants
• Usually leave sticky traces on the bitten areas, which are visible to the naked eye

iv) Cucumber wilt

• Especially for greenhouse plants!
• Rapid death of plants starting from yellowing leaves
• Easily recognizable by the clear wilting of the leaves in connection with the yellow discoloration

v) Leaf spot disease

• Fungicidal infestation, leaf death
• Starting with yellow spots on the upper side of the leaves, which quickly change color to a recognizable brown

vi) Verticillium wilt

One of the most serious diseases is Verticillium wilt, triggered by fungi. Unfortunately, if an infection took place, you must remove the entire plant and burn it or dispose of it in the household waste.  The germs can stay in one location for up to ten years. Hot weather favors infection. The symptoms are:

• Leaves turn yellow
• Begin to wither
• Plant will slowly die

As soon as your cucumber plants wilt without any apparent reason from the summer heatwave and present yellow leaves, you must assume the infection. Pests are not responsible for this.

vii) Leaf spot disease

Cucumis sativus can suffer from leaf spot disease, which is caused by various bacteria, viruses, or fungi. The reason for this is wet leaves, a location that is too damp or aphids. These are first recognized by yellow spots on the upper side of the leaves until they turn brown and die. You can only remove the leaves and, as with the cucumber mosaic virus, do not dispose of them in the compost.

3. Pests on the cucumber plant

Equally dangerous for Cucumis sativus are pests that can occur outdoors and in greenhouses. Two pests occur, of which the aphids (Aphidoidea) are much more dangerous because they transmit diseases. Aphids can be recognized by the yellowed and stunted foliage, as well as by the honeydew and, rarely, by ants. You need to be quick about an aphid infestation as they often make short work of a cucumber plant. Fortunately, classic home remedies can be used:

• Neem oil
• Sprays made from water and milk
• Beneficial insects such as ladybugs or lacewings

Affected areas can also be removed. Aphids are difficult to prevent. Because of this, you must always be on your guard. In the greenhouse, spider mites (Tetranychidae) are among the cucumber pests.

These can be recognized by the webs between the leaves and axes, as well as bright spots on the foliage. The leaves then turn from brown to yellow and become drier and drier. Spider mites appear when there is too much drought and cucumber plants are planted too close together. The following measures will help combat:

• Remove affected plant parts
• Neem oil
• Beneficial insects such as predatory mites or gall midges
• water jet

Spider mites, while stubborn, don’t transmit disease, making infestations less of a concern.

Measures against yellow cucumber leaves

Anyone who recognizes that the cucumber leaves have already turned yellow would of course want to save their plants as much as possible so that they can still enjoy the longed-for fruits. Leaves that are already infected and have turned yellow can usually no longer be saved and can therefore safely be ignored. Therefore, attention should always be paid to eliminating the causes of the discoloration:

i) Nutrient deficiency:

One of the most typical causes of yellow cucumber leaves is nutrient deficiency. Since cucumbers are heavy feeders, they must be constantly supplied with nutrients to satisfy the hunger of the plants. The mistake is often made of using a mineral or artificial fertilizer, which does not get the cucurbits at all.

You just can’t draw energy from these. It is particularly important to prepare the site before planting with a suitable long-term fertilizer that is mixed directly into the soil. Suitable for this:

• Mature compost
• Horse manure (rotting)
• Cattle manure (rotting)
• Cucumber fertilizer from the specialist trade
• Organic fertilizer

Cow dung as a wound closure Simply add a good portion of these to the excavation or follow the manufacturer’s instructions. The long-term effect is particularly important since it does not help much to fertilize cucumbers at regular intervals.

The soil must deliver the nutrients to the cucumber plant. For this reason, it is necessary to fertilize again in July if no slow-release fertilizer has been used. The plants are particularly dependent on magnesium.

ii) Dryness:

Since the cucumber plant comes from the Indian subcontinent, they depend on an adequate water supply. A dry location is not recommended and causes yellow discoloration of the leaves. In addition, the fruits can take on a bitter aroma due to drought. They depend on a permanent water supply, which is made possible in the following ways:

• Water daily
• Time: in the morning
• Use rainwater
• Lukewarm and stale
• Only water the root area
• Never water the plant directly

Alternatively, you can apply a layer of mulch if it’s very hot and dry over the summer. The mulch layer protects the cucumber plant from drying out. If you find a specimen with yellow leaves and a dry location, water it vigorously.

iii) Draft:

This cause applies not only to specimens in greenhouses. Cucumbers do not tolerate strong winds outdoors or cold air in the greenhouse. So make sure that the little plants are protected in the bed and don’t get a cool breeze. If the specimens are in the greenhouse, do not forget to close the ventilation, such as open doors or windows, in the evening and open them again in the morning. This provides enough air without exposing the plants to dangerous drafts.

iv) Fungal infestation:

For example when powdery mildew or leaf spot disease occurs: use chemical fungicides (e.g. Compo Duaxo universal fungicide),

Proven household remedy: spray the plant and in particular the affected leaves with skim milk

v) Aphid infestation:

Control with chemical insecticides (e.g. Celaflor Cairo), alternatively use nettle manure or soap solution for repeated spraying

Viral diseases, such as cucumber mosaic viruses: the affected plants are usually removed immediately to avoid transmission to neighboring plants, it is not possible to combat viruses!

In case of being in the Greenhouse

When the plants are flowering and bearing fruit, they should be watered every 2-3 days on average. 1 bucket of warm water is poured under each bush (in case of no cold). When it is hot outside, the watering frequency will be increased, when it is cool and rainy, it will be reduced. You can tell if you need to water if you carefully dig up the soil between two adjacent bushes: if it is not dry, then the procedure will not be carried out.

• Mulch the soil around the bushes so that it does not dry out quickly and weeds do not grow on it.
• Keep the temperature at an optimal level. Cucumbers feel most comfortable when the temperature in the greenhouse or greenhouse is maintained at 25-30 ° C during the day and 18-20 ° C at night. If the temperature falls below 17 °C or rises above 40 °C, this immediately affects the plants, and the formation of ovaries stops.
• Ventilate the greenhouse frequently. This will help protect plants from downy mildew and other fungal diseases.
• Feed the plants in time. It is advisable to use ready-made complex fertilizers: in most cases, this is enough to provide cucumbers with all the nutrients they need.
• Treat “wards” with pesticides. As soon as signs of diseases or pests appear, the plants should be immediately sprayed with appropriate preparations. If viral diseases are found, pull out and eliminate the infected bushes. There is no need to wait for problems to arise, but to take preventive measures immediately.
• If you follow the rules of growing cucumbers in hotbeds and greenhouses, you can avoid many troubles, including yellowing.

In the open field

The general principles of caring for cucumbers both in greenhouses and in open beds are similar. In any case, they must be properly watered, fertilized, formed, protected from diseases and pests, and harvested on time. For cucumbers growing in beds in open ground, in addition to the measures listed above, you will need:

• In spring, cover them with spun-bond, foil, or some other lightweight material to keep them from freezing.
• Do not water the bushes during the day, in the heat, it is better to do this in the morning or the evening.
• Pour water at the root, try not to get on the cucumbers themselves.
• Carefully pull up the weeds so as not to damage the shallow root system of the bushes.

You can prevent the yellowing of cucumber plants in open beds with these simple measures.

Solution For Why Succulent Leaves Turning Black 

Solve yellow cucumber leaves with home remedies

Drying of the green cover, associated with the appearance of yellow spots, is a sign of fungal infection. Most of the dressings described above can not only improve the development of growth but also maintain its health. Let’s add to the list of recipes for combating plant diseases.

i) Milk soap composition

The solution is prepared from a bucket of water, a liter of milk or yogurt, a tablespoon of grated laundry soap, and 30 drops of iodine tincture. Add soap lastly and make sure it dissolves completely. The frequency of preventive treatment is 10 days. Spraying is carried out after the appearance of 4-5 leaves.

ii) Serum

Against powdery mildew, you can use the recipe described above, or simply dissolve 2 liters of whey in a bucket of water. Such spraying will not cause harm even with daily use. To prevent late blight in the greenhouse and the open ground, it is recommended to carry out processing every 5-6 days, to not to provoke high humidity.

iii) Lemonade

Every house has baking soda, so making a composition for killing fungal spores is easy. Dissolve a tablespoon of vegetable oil and soda in 5 liters of warm water, add an aspirin tablet and mix thoroughly. To avoid burning the bush, process it only in the absence of the sun. For pouring, dissolve a tablespoon of baking soda in a bucket of water.

iv) Potassium Permanganate

If you find signs of illness, move a 1% solution of potassium permanganate. Spray the bushes with the mixture.

Prevention instead of rescue

Precisely because it is so difficult to combat damage to cucumbers that have already begun, it makes sense to do everything possible from the start to avoid the disease or damage. In addition to ensuring optimal environmental conditions, in greenhouses as well as outdoors, this also includes good protection against pathogens and parasites.

This is initially achieved through suitable protective measures, such as fly screens in front of the greenhouse windows or insect nets over the outdoor plants. In addition, the risk of infection can be easily and effectively prevented by using germ-free soil. It should be pointed out at this point, however, that despite all measures, there is always a risk of illness.

To prevent the appearance of yellow leaves on cucumbers, you must:

• For those that grow in the open air, choose a place so that they are in the sun for the first half of the day, and in partial shade for the second. This allows the plants to take a break from the heat of the day.
• Do not plant cucumbers after pumpkin seeds to protect them from joint diseases.
• Watch the crop rotation and return the plants to the beds only after 3-4 years.
• Plant the bushes according to the scheme recommended for each variety, do not thicken the planting.
• Pour warm water under the root, not over the leaves.
• Whitewash the greenhouse roof with chalk solution to lower the temperature inside.
• Do not forget to fertilize the cucumbers, apply the dressings only in the doses recommended by the manufacturer.
• Remove diseased and aging leaf blades.
• Preventive spraying with an herbal infusion of ash or milk whey with iodine, infusion of onion peel, 1% solution of potassium -permanganate and other folk remedies.

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